[TowerTalk] FIRST TOWER & 2ND FLOOR SHACK --HELP

[Earl Morse]

Sure there are better places to put the polyphasers.  My own are located where the coax penetrates from outside to inside the building.  The point was that they need to be put at the "boundary" between "in the shack" and "outside the shack".  If that boundary is extended by a conductive conduit from the shack out to the base of the tower or even to the top of the tower then they could be placed at those points.  Probably not optimal but feasible.  Any breaches in that boundary such as one unpolyphasored coaxial feed, an unbypassed rotor cable/control line, or an unfiltered power mains defeats the whole lighning protection system.  I can't see how it would be easier or cheaper to run conduit to the top of a tower so for my money the feedline entrance point is the way to go (better and cheaper, my favorites).

My system utilizes grounding blocks at the top and bottom of the tower for all the cabling and polyphasors where the cabling enters the building.  I have lots of ground rods but didn't do the Ufer ground as the installation is in a wetlands and soil conductivity is excellent.  Its also a pier pin installation.  

Earl
N8SS

------------------------------

Message: 3
Date: Wed, 07 Aug 2013 10:56:39 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] FIRST TOWER & 2ND FLOOR SHACK --HELP
Message-ID: <52028A57.205 at audiosystemsgroup.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 8/7/2013 9:59 AM, Earl Morse wrote:
>   Whether you run the conduit to the top of the tower and put your polyphasers at that point OR run the conduit to the base of the tower and place the polyphasers at that point OR run conduit through the house and place the polyphasers at the entrance point its all about providing that alternate path for lightning that doesn't pass through your hamshack.

It DOES matter where Polyphasers are located -- their function is to 
protect the equipment to which they are connected, and they work by 
shorting the center conductor of the coax to the shield. For that 
reason, they should be as close to the equipment as practical.

That is VERY separate from the issue of grounding, which is the most 
critical aspect of lightning protection. I think most experts would 
advise that the cables go down the tower all the way to its base, be 
bonded to the tower at the top and bottom, and go along or in the ground 
to the house, where they should be bonded to the building ground, then 
come up to the shack. There must also be a bond from your shack ground 
to the building ground.

The tower itself must be grounded at its base, both to it's own concrete 
base (a Ufer ground) and to at least three rods, usually each bonded to 
a leg.  This provides a short (low inductance) path to earth for a 
strike, which minimizes what is coupled to your home.

Remember -- lightning is not a DC event, it is an RF event, with its 
energy broadly centered around 1 MHz, and extending for at least one 
decade of frequency above and below. (that is, 100 kHz to 10 MHz). So 
what matters most is the inductance and the routing of the grounding 
conductors, not their resistance. And remember also that lightning comes 
into our homes from the power system, the telephone system, CATV 
systems, and on the wiring in our homes, so all of this stuff must be 
bonded together and to that central ground, usually at the point were 
power comes into the house.

Finally, radios do not need "an RF ground" to work, to be safe, or to 
minimize noise or RFI.  But they DO need proper bonding, as I've 
described for lightning safety, and proper bonding can often help with 
noise and RFI.

73, Jim K9YC


------------------------------